Display panels in the form of array of cells, where individual cells contain electrically deformable material, are known in the art. Patent publication WO 01/48531, for example, discloses display panel structures where the cells each comprise two deformable dielectric layers, which meet at a common interface. One of said dielectrics can be air, the other is preferably a polymer material acting as a relief forming gel. For each cell, there is a first electrode structure, a support electrode structure is arranged on one side (below) of said dielectric layers, and a second electrode structure, a signal electrode structure on the other side (above) of said layers, there being means for providing signals to the signal electrodes in order to create electric fields through the two dielectric layers and to further create surface reliefs on the gel surface at the interface of said two dielectrics. The periodical, typically sinusoidally varying reliefs created on the gel surface in each of the cells allows under the effect of light from a light source to create images on the display panel, which are viewable by the naked eye.
The major shortcomings of such light modulators may be associated with the practical difficulties in producing desired gel relief profiles with good precision. This, of course, impairs the light modulating capabilities of the individual pixels or cells. Especially in the case of portable devices, the power consumption also becomes very important. The increase of diffraction amplitude of the gel relief typically also increases the power consumption.
With the goal of bringing display quality closer to that of a paper print, for example, the brightness and contrast of the displays must be further improved. In order to allow the use of display devices in small-size portable devices, the power consumption and thickness of the display devices should also be further reduced. To make mass production of portable devices possible, the manufacturing technology of the display devices should be simple in order to allow lower prices. The displays should also have short response times to be able to display video or similar fast changing image content without degration of the image quality. The aforementioned requirements also apply on other light modulator devices than display panels. Other applications which may be based on the use of electrically controlled deformation of dielectric and viscoelastic transparent materials include, but are not limited to, electrically controlled diffractive or refractive lenses, or electrically reconfigurable optical waveguide couplers.
In an earlier patent application PCT/FI02/00512 (now published under WO 2003/107087), the Applicant has already proposed a novel electrode configuration for light modulator cells based on the use of dielectric and viscoelastic materials to facilitate enhanced and active deformation of the viscoelastic material. The basic idea of said electrode configuration is to utilize active fieldshaping enhancement electrode structure located in the proximity, and in addition, to the traditional signal electrode structure of a cell in order to affect the electric field between the signal electrode structure and the support electrode structure and through the viscoelastic layer in a manner that the deformation amplitude of the viscoelastic layer in the cell is increased. The enhancement electrodes may have with respect to the signal electrodes, for example, an in-plane-type configuration or a sandwich-type configuration. The various embodiments of the enhancement electrode configurations are explained in more detail in the aforementioned earlier application.
The enhancement electrodes according to PCT/FI02/00512 can, among other things, increase the diffraction efficiency of the light modulator cells, shorten the response time required to switch a cell (pixel) between on and off states, and reduce the voltage levels required for a defined diffraction amplitude, that is for a certain height of a gel relief. Therefore, the developments described in said patent application aim to the manufacturing of light modulators with better optical contrast, higher switching speed and smaller power consumption.